Few things I've learned traveling in 100° plus temps.
One of the simple fridge fans can make a big difference, I put so it "blows" over the fins inside the fridge.
Do not place items that are not pre-cooled in the fridge. We try to freeze and pre-chill everything before we load it. I've found that laying frozen water bottles on the bottom of the freezer seems to help keep everything cool.
We take a cooler for all beverages, rotate water bottles in/out of the freezer.
Limit opening the fridge as much as possible.
If you are parked with your fridge facing the sun during the hottest part of the day try to provide some shade. In our case we made an awning shade to keep the sun off of that sidewall. Made a big difference. Not much you can do if you are driving and the fridge wall is getting beat down by the sun, other then change your driving time.
Run on propane, it seems to do a better job keeping the fridge/freezer cool.
